One way to defend your personal space is to carry a halberd while wearing a Strawberry Shortcake t-shirt but no pants. Not everyone, oddly enough, is comfortable with this approach. For them, Zac Ong may have a solution. His project, entitled Repel, features a rotating shoulder-mounted laser. When it detects that people have entered his personal space, it alerts him with LEDs and buttons that blink and spin with increasing speed as the intruder approaches.